<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>用键盘控制DIV</title>
    <style type="text/css">
    html,
    body {
        overflow: hidden;
    }
    
    body {
        margin: 0;
        padding: 0;
    }
    
    pre {
        color: green;
        padding: 10px 15px;
        background: #f0f0f0;
        border: 1px dotted #333;
        font: 12px/1.5 Courier New;
        margin: 12px;
    }
    
    span {
        color: #999;
    }
    
    #box {
        position: absolute;
        top: 50px;
        left: 300px;
        width: 100px;
        height: 100px;
        background: red;
    }
    </style>
    <script type="text/javascript">
    window.onload = function() {
        var oBox = document.getElementById("box");
        var bLeft = bTop = bRight = bBottom = bCtrlKey = false;

        setInterval(function() {
            if (bLeft) {
                oBox.style.left = oBox.offsetLeft - 10 + "px"
            } else if (bRight) {
                oBox.style.left = oBox.offsetLeft + 10 + "px"
            }

            if (bTop) {
                oBox.style.top = oBox.offsetTop - 10 + "px"
            } else if (bBottom) {
                oBox.style.top = oBox.offsetTop + 10 + "px"
            }
            //防止溢出
            limit();
        }, 30);

        document.onkeydown = function(event) {
            var event = event || window.event;
            bCtrlKey = event.ctrlKey;

            switch (event.keyCode) {
                case 37:
                    bLeft = true;
                    break;
                case 38:
                    if (bCtrlKey) {
                        var oldWidth = oBox.offsetWidth;
                        var oldHeight = oBox.offsetHeight;

                        oBox.style.width = oBox.offsetWidth * 1.5 + "px";
                        oBox.style.height = oBox.offsetHeight * 1.5 + "px";

                        oBox.style.left = oBox.offsetLeft - (oBox.offsetWidth - oldWidth) / 2 + "px";
                        oBox.style.top = oBox.offsetTop - (oBox.offsetHeight - oldHeight) / 2 + "px";

                        break;
                    }
                    bTop = true;
                    break;
                case 39:
                    bRight = true;
                    break;
                case 40:
                    if (bCtrlKey) {
                        var oldWidth = oBox.offsetWidth;
                        var oldHeight = oBox.offsetHeight;

                        oBox.style.width = oBox.offsetWidth * 0.75 + "px";
                        oBox.style.height = oBox.offsetHeight * 0.75 + "px";

                        oBox.style.left = oBox.offsetLeft - (oBox.offsetWidth - oldWidth) / 2 + "px";
                        oBox.style.top = oBox.offsetTop - (oBox.offsetHeight - oldHeight) / 2 + "px";

                        break;
                    }
                    bBottom = true;
                    break;
                case 49:
                    bCtrlKey && (oBox.style.background = "green");
                    break;
                case 50:
                    bCtrlKey && (oBox.style.background = "yellow");
                    break;
                case 51:
                    bCtrlKey && (oBox.style.background = "blue");
                    break;
            }

            return false
        };

        document.onkeyup = function(event) {
            switch ((event || window.event).keyCode) {
                case 37:
                    bLeft = false;
                    break;
                case 38:
                    bTop = false;
                    break;
                case 39:
                    bRight = false;
                    break;
                case 40:
                    bBottom = false;
                    break;
            }
        };

        //防止溢出
        function limit() {
            var doc = [document.documentElement.clientWidth, document.documentElement.clientHeight]
                //防止左侧溢出
            oBox.offsetLeft <= 0 && (oBox.style.left = 0);
            //防止顶部溢出
            oBox.offsetTop <= 0 && (oBox.style.top = 0);
            //防止右侧溢出
            doc[0] - oBox.offsetLeft - oBox.offsetWidth <= 0 && (oBox.style.left = doc[0] - oBox.offsetWidth + "px");
            //防止底部溢出
            doc[1] - oBox.offsetTop - oBox.offsetHeight <= 0 && (oBox.style.top = doc[1] - oBox.offsetHeight + "px")
        }
    };
    </script>
</head>

<body>
    <pre>
红色方块为键盘操作区域，您可以进行如下操作：

上：↑ 下：↓ 左：← 右：→

Ctrl + 1 : 背景变为绿色
Ctrl + 2 : 背景变为黄色
Ctrl + 3 : 背景变为蓝色
Ctrl + ↑ : 放大
Ctrl + ↓ : 缩小
</pre>
    <div id="box"></div>
</body>

</html>
